"32GB (29GB available after system setup)"
It's got nothing to do with system setup, they're just explaining which units they're using.

The Nintendo Direct explained (in Japanese) that 32GB (32 Gigabytes) is 29.8GiB (29.8 Gibibytes)

32 * 1000 * 1000 * 1000 = 32,000,000,000
32,000,000,000 / (1024 * 1024 * 1024) = 29.80